A variety of gripping compositions have been applied to outsoles of boots and shoes in order to improve the slip resistance of such footwear under slippery conditions such as ice or snow. Early patents proposed, for example, securing an abrasive anti-slip patch onto a sole bottom (see Roodhouse U.S. Pat. No. 1,796,399 issued Mar. 17, 1931) or providing a sole (Vicente U.S. Pat. No. 2,031,196 issued Feb. 18, 1936.) Particles of grit such as silicon carbide or sand have been secured to a sole bottom with conventional adhesives. See, for example, Bell, U.S. Pat. No. 4,160,331 issued Jul. 10, 1979. Textured anti-slip soles are well known. See, e.g., Vistins, U.S. Pat. No. 4,151,662 issued May 1, 1979 and Dassler, U.S. Pat. No. 3,555,697 issued Jan. 19, 1971. Overshoes having gripping elements such as aluminum screens and rubber pads have also been proposed, as disclosed in Hayden Jr., U.S. Pat. No. 4,446,635, issued May 8, 1984. Most of these designs have proven impractical or economically infeasible, and are not currently in commercial use.
Other known nonslip particles have been made by embedding particles such as aluminum pieces or shavings or pieces of porous material in a matrix of rubber or resin. See, for example, Mitchell, U.S. Pat. Nos. 3,573,155 issued Mar. 30, 1971, 3,629,051 issued Dec. 21, 1971, and 3,802,951 issued Apr. 9, 1974, as well as Japanese Patent Publication No. 61-166710. These systems generally require the entire sole to contain the particulate material, even though only the particles or pieces exposed on the outer surface of the sole actually provide anti-slip effects.
The foregoing patent to Bell describes a shoe having inset layers of grit on the bottom of the sole. Such a sole does not require the grit to be distributed throughout the entire sole, but suffers from poor durability. Specifically, inorganic grit particles have a poor affinity for rubber, and the grit layers tend to break off easily when simply glued to the sole bottom. The present invention provides an improved gritted outsole which addresses this problem.